Having installed a portable build of Strawberry 5.20.0, how do I then
alter $Config{libpth} - such that the alteration to $Config{libpth} is
already in place every time I open up an instance of the strawberry shell ?

For my own Windows perls, I would do this by editing appropriately the
libpth entry in Config_heavy.pl and Config.pm, but Stawberry seems to be
reading libpth from some other source(s) as the entries in
Config_heavy.pl and Config.pm don't even match $Config{libpth}.
And changing the libpth entries in those 2 files doesn't seem to be
having any effect at all.